To investigate the relation between different types of exposure to noise and a classic sign of noise-induced hearing loss (NIHL); the audiometric notch.

A cross-sectional epidemiological survey was carried out in electronics sound inspectors exposed to continuous and impulsive type noises. The noise levels in the working environments, and the audiometric hearing threshold levels were measured.

Electronics sound inspectors were exposed to impulsive noise ranging from 74.1 to 88.9 dBA. The hearing loss induced by impulsive noise was greater and was characterized by maximum loss at 6 kHz audiometric frequency, as opposed to the notch at 4 kHz that is typical of continuous noise.

The results suggest that the probable effect of impulsive noise on hearing should be considered even when the exposure is within the 85 dB equivalent A-weighted level. To diagnose NIHL it is important to elicit a detailed and accurate history of exposure to noise. Although the notch at 4 kHz is a well established clinical sign and may be valuable in confirming the diagnosis, the 6 kHz notch is variable and of limited importance.